NEW MATERIAL: Metallocene compounds including monocyclic polycyclic ligands of a single cyclopentadienyl, respectively combined with a Group IVB transition metal atoms, and ligands of hetero atoms of a Groups VA or VIA elements.

EXAMPLE: Dimethylsilyltetramethylcyclopentadienyl-tert-butylamide zirconium dichloride.

USE: Components for olefin polymerization catalysts. Catalyst systems obtained by the combination with alumoxanes, give polyolefins having a high weight average molecular weight, narrow distribution of molecular weight, and low concentration of catalyst residue.

PROCESS: A cyclopentadienyl lithium compound is reacted with a dihalide first, and then the product is reacted with a lithium amide salt. Then the product is reacted with an alkyl lithium reagent to obtain a dilithium salt of a cyclopentadienyl compound, and the same is reacted with a Group IVB transmition metal halide.